Device for measuring distances, distance measurer and stop element therefor

ABSTRACT

The invention relates to a device for measuring distances comprising a distance measurer ( 1 ) and a stop element ( 3; 3′; 3 ″) enabling precise and mechanically stabile fixed installation on any form of top surfaces. Interchangeable stop elements ( 3; 3′; 3 ″) are disposed on a distance measurer ( 1 ), and embodied on the side thereof which is orientated towards the object to be measured in such a way that exact installation can take place on the surface of the object. Another use of the stop element is that it can comprise a receiving element for securing a distance measurer ( 1 ), whereby the distance measurer is pivotally mounted about at least one horizontal rotational axis ( 12 ) whilst the distance measurer ( 1 ) is in use. The stop element ( 3 ″) is formed in such a way that it is possible to adjust the device and subsequently measure different measuring points (C,D) without having to take geometric changes into account as a result of said adjustment.

[0001] The invention relates to a device for measuring distancesaccording to the preamble of claim 1, and a distance-measuringinstrument for this device according to the preamble of claim 5 and astop element for this device according to the preamble of claim 7.

[0002] Devices for measuring distances, comprising a combination of adistance-measuring instrument, preferably a laser distance-measuringinstrument, and a holder for positioning and for fixing thedistance-measuring instrument, are generally known and are used in manyareas. These holders effect exact positioning of the distance-measuringinstrument relative to a reference point, so that various measurementscan be transferred to a common reference system. Moreover, they ensurestable retention during the measuring process.

[0003] A point which serves as a reference point for measured distances,is to be defined here as the reference point, i.e. all values actuallymeasured by the distance-measuring instrument must be converted so thatthey correspond to the distances in the reference system. As a rule, inthe case of an installation at a point, for example at a wall in abuilding, it is therefore also necessary to take into account thehousing parts of the distance-measuring instrument and any installationparts which serve for positioning the distance-measuring instrument.

[0004] The holders of the prior art are generally in the form of tripodsand the distance-measuring instrument is fastened by means of a threadand threaded bush, mobility about two axes (horizontal and vertical)generally being ensured. This type of holder is used in particular inthe area of geodetic surveys.

[0005] In other areas, too, it is necessary to install thedistance-measuring instrument on an object or a reference point in adefined manner in order to permit an exact measurement of the distanceto another object. In particular, use in the construction sectorrequires a high accuracy of measurement in the case of a very wide rangeof surfaces and reference points. Examples of such measurements arebuilding spacings, ceiling heights and internal diameters of openings.Owing to the building structures, measurements frequently also have tobe carried out from corners, resulting in particular requirements withrespect to size and handling properties of the distance-measuringinstrument. The frequently highly structured ground gives rise toproblems with the exact installation and hence the positioning of thedistance-measuring instrument. For example, holes, edges, rounded areasor wire meshes make it more difficult to position the device exactly. Itmay also be of interest to be able to survey liquid levels, for examplethe water level in a space; however, the surveying of liquid surfaces bymeans of the distance-measuring instruments of the prior art is notpossible without complicated aids.

[0006] The main requirement with regard to the holder is thus associatedwith the positioning of the distance-measuring instrument relative to apoint or in a plane, by means of which the various measurements can betransferred to a standard reference system. Moreover, the achievableaccuracy during the measuring process can be increased by mechanicallyfirm fixing.

[0007] The main difficulties here are the defined installation at thereference point to be surveyed and the mechanically sufficiently stablefixing of the device during the measurement on the object. A definedinstallation can be realized only with difficulty particularly in thecase of poorly accessible points, such as, for example, in angledsurfaces, or in the case of objects having a disadvantageous surface,such as, for example, a very soft or curved surface. In addition to theaccessibility of the measuring point, which can be ensured, for example,by a simple, hinged spike, there is a requirement for secure fixing ofthe measuring device during the measurement. Aids necessary for thispurpose frequently result in a deviation from the ideal installation atthe measuring point. The distance-measuring instrument must bepositioned with the aid of a holder or a supporting construction. If thedistance-measuring instrument cannot be installed therewith directly atthe point actually to be surveyed, at least the distance from the actualmeasuring location to this point must be known.

[0008] If a measuring stop is used for the installation, as can also beassumed to be known from other areas of measurement technology, thisadditional distance of the measuring point, produced by the measuringstop, must be taken into account in the measurement.

[0009] The realization of such a measuring system is subject to variousspecifications. The requirements with regard to the measuring device aregood handling properties, the necessary precision and a small size whichmakes it possible to reach and to survey all relevant areas.

[0010] The generally hand-held laser distance-measuring instruments usedfor this purpose are widely employed. A device of this type isdescribed, for example, in EP 0 738 899 B1.

[0011] The exact positioning of the distance-measuring instrument on theobject to be measured generally proves problematic. Thus, for example,the measurement of a distance between a smooth wall and pipe requiresthe installation of a distance-measuring instrument on a curved surfaceif the advantage of a wall as a flat reflecting surface is to beretained.

[0012] It is the technical object of the present invention to provide adevice and its components comprising distance-measuring instrument andstop element, which ensure defined and sufficiently fixed installationof the distance-measuring instrument on surfaces of virtually anydesired shape.

[0013] This object is achieved, according to the invention, by thedefining features of claims 1, 5 and 7. Advantageous and alternativeembodiments and further developments of the device are evident from thefeatures of the subclaims.

[0014] In the subject of the invention, an exchangeable stop elementwhose side facing the object from which the measurement is to beeffected can be substantially adapted to said object is mounted ona—preferably hand-held—distance-measuring instrument. Thus, both exactpositioning relative to the reference point to be surveyed and firmmounting on the surface can be achieved.

[0015] The separation of measuring point and reference point which iscaused by the positioning of the measuring device necessitates acorrection of the distance given by the distance-measuring instrument.This correction can be automatically calculated by an integratedcomputer if the required dimensions of the stop element are exactlyknown as correction data.

[0016] In principle, it is also possible, in an alternative realization,to dispense with an integrated computer and to calculate the requiredcorrection externally on the basis of the specified data of the stopelement.

[0017] It is also possible in principle to use the device according tothe invention to calculate the distance to a plurality of referencepoints simultaneously with a single measurement.

[0018] The substantially freely designable object side of the stopelement makes it possible to provide stop elements for all shapes andsurfaces. Even the use of a float as a stop element for measuring thedistance from liquid surfaces to reference objects can be realized.

[0019] A version which is particularly easy to handle is a stop elementproviding adjustable and universally applicable installation. This maybe, for example, in the form of a telescopic arm which, after itsinstallation on the object to be surveyed, automatically measures itslength and automatically transmits this value for calculation of thecorrection.

[0020] A further advantageous possible use is the calculation ofdistances to points which are basically inaccessible, such as, forexample, pipe axes. A diameter-specific collar as a stop element makesit possible to mount the measuring device on a pipe. The measured valuecan then be corrected directly so that the distance to the middle of thepipe is output. By means of this procedure, the computational effort andtime requirement are substantially reduced, particularly in the case ofrelatively large measurement series. The collar may be designed to beadjustable, as in the above example of the telescopic arms.

[0021] A further advantageous possible use of the exchangeable stopelement is its use as a stop element for a holder which serves as aninstallation point for measurements. In geodetic applications, a tripodstand is generally used here as a mount and holder for thedistance-measuring instrument. Here, the mounted distance-measuringinstrument is mounted so as to be rotatable about a vertical axis, sothat a plane which can generally be levelled by adjustment facilities inthe tripod stand is defined by the movement about this axis.

[0022] For surveys of two or more points which are outside thishorizontal rotational plane of the distance-measuring instrumentrelative to the holder, the distance-measuring instrument must bepivoted about a horizontal axis. By means of a measurement of two pointslocated one on top of the other, the height difference can in principlebe determined.

[0023] The present state of the art for holding laser distance-measuringinstruments comprises a threaded bush which is perpendicular to theemission axis of the distance-measuring instrument and which is engagedby a screw of the stand mount. Measuring device and stand are connectedto one another in this way so that the distance-measuring instrument ismounted so as to be rotatable about an axis passing through thisconnection and oriented perpendicular to said distance-measuringinstrument.

[0024] Since, in the case of mounts of this design, the axis of rotationand the axis of laser emission or of laser detection have no commonpoint of intersection, pivoting results in differing positioningsbetween the reference points of distance-measuring instrument andtripod, which have to be compensated computationally for highly accuratemeasurements.

[0025] It is the technical object to provide a device which makes itpossible to attach a distance-measuring instrument to a mount—preferablya tripod—so as to be rotatable about a horizontal and a vertical axis,so that the pivot movement does not give rise to any corrections of themeasured distances.

[0026] This object is achieved, according to the invention, by thedefining features of claim 10. Advantageous embodiments and furtherdevelopments of the device are evident from the features of thesubclaims.

[0027] In the subject of the invention, a device for measuring distanceswhich is fastened to a holder is formed from a—preferablyhand-held—distance-measuring instrument and a—preferablyexchangeable—stop element. The stop element is mounted on thedistance-measuring instrument in such a way as to ensure a mechanicallystable connection between distance-measuring instrument and holder,which connection is pivotable about at least one axis relative to theholder.

[0028] According to the invention, this stop element effects positioningof the distance-measuring instrument relative to the holder so that thepoint of intersection of all axes of rotation of the distance-measuringinstrument relative to the holder lies on an axis or between a pluralityof axes of beam paths used for the distance measurement.

[0029] If axes of rotation and axes used for the distance measurementintersect at a point, this can be used as a reference point of thedistance measurement and a correction can be omitted. If the point ofintersection of all axes of rotation lies between a plurality of axes ofbeam paths used for the distance measurement, there are in principlestill slight deviations due to pivot movements, but these can beneglected in the case of beam paths which are sufficiently close to oneanother.

[0030] A possible, exemplary realization of a stop element according tothe invention comprises the mounting of a straight stop element on thatside of a commercial, hand-held laser distance-measuring instrumentwhich is opposite the laser emission. The stop element is mounted on astand by means of thread and threaded bush so that an axle mounted onthe stop element—for example a hinge—lies in the axis of the beam pathused for the distance measurement.

[0031] The main requirement with regard to the stop element thus relatesto the positioning of the distance-measuring instrument relative to oneor more axes of rotation, which in principle can be located on the stopelement or on the holder.

[0032] A difficulty here is the defined installation at the referencepoint defined by the point of intersection of the axes. Since, owing tothe stop element, the distance-measuring instrument cannot be installeddirectly at the reference point, the additional distance to this point,produced by the stop element, must be known.

[0033] The electronics required for the calculation can in principle beimplemented as an analog circuit or as a digital computer in the device.A correction can then be effected by a modification of the circuit or bycalculation using correction data in the digital computer. Thecorrection data can in principle be polled at the beginning of ameasuring process and input manually or read in automatically and, aftertemporary storage in the computer, used repeatedly for calculations.

[0034] However, constant polling for each newly required calculation canalso be realized. Automatic identification of the stop element withreading in of the correction data is a particularly advantageous designsince it is user-friendly.

[0035] If, according to the invention, the device has the means forcalculating the correction, either the corrected value directly or therequired correction distance can be specified. If the stop element hasan automatically detectable identifier, the distance-measuringinstrument recognizes the element mounted in each case and canindependently calculate the correction without additional inputs afterinstallation on the object. The required data of the stop element can bestored in said element itself or in the distance-measuring instrument.Furthermore, the means for calculating the corrected distance or thenecessary correction distance can in principle be housed both in thedistance-measuring instrument and in the stop element or in both partstogether.

[0036] The location of data storage and calculation of the correction isdependent on the exact design of the device. It is therefore possible torealize a standardized distance-measuring instrument on which it ispossible to mount complex, multiply adjustable stop elements which areoffered by a very wide range of manufacturers, in some cases exclusivelyfor highly specialized applications. For this group, calculation in thestop element has the advantage of being able to store all necessary andmanufacturer-specific data exclusively in the exchangeable stop elementand of acquiring only the measured distance from the comparativelystandardized measuring device. However, this solution is disadvantageouswith regard to the complexity of the stop element.

[0037] The other possibility, calculation in the distance-measuringinstrument, has the advantage of the simple, economical stop elementsbut necessitates storage of the type-specific data in thedistance-measuring instrument or storage in the stop element andtransmission to the measuring device. However, this solution hasadvantages if it is intended to employ a stop element having adjustablecomponents, since the current settings or correction values then have tobe transmitted in any case.

[0038] The identification of the stop element can in principle beeffected in various ways, it being possible to realize bothstraightforward recognition of the stop element without storage ofinformation and transmission of data stored in the intelligent stopelement.

[0039] For example, the respective type of stop element can berecognized purely mechanically and without data storage in this elementfrom the design of the plug connector. Identification could be effectedhere, for example, by means of a special plug in a component and thepositions of a plurality of pins in the other component in each case,the presence or absence of pins in their positions ensuring binarycoding.

[0040] A further possibility comprises mounting of magnets, from theposition of which it is possible to conclude the type of stop element.The detection of the magnets can be effected, for example, using theHall effect.

[0041] On the other hand, for example, electronic variants permit theuse of integrated circuits and memory modules on which a larger numberof data can be stored in the stop element and can be read out whenrequired by the measuring device. The same applies to optical orelectromagnetic storage media, for example magnetic stripes. Thetransmission of the data can be effected, for example, by electricalcontacts or via electromagnetic radiation, for example by means of aresonant circuit. The last-mentioned possibility has the advantage thatthe stop element can be designed without external contacts, with theresult that a tighter seal between distance-measuring instrument andstop element can be realized in a simple manner so that the influence ofexternal conditions, such as, for example, tough physical ambientconditions due to humidity or dust, on the use of the instrument isreduced.

[0042] It is the object of the device according to the invention toachieve substantially improved handling and reduced time requirement incombination with the same or improved precision of the distancemeasurement.

[0043] The device according to the invention is described in more detailbelow, purely by way of example, with reference to embodiments shownschematically in the drawing. Specifically,

[0044]FIG. 1 shows an overall diagram of a device comprisingdistance-measuring instrument having two exchangeable stop elements,

[0045]FIG. 2 shows an exemplary application of the device having aspecially shaped stop element which, for example, permits installationon a pipe,

[0046]FIG. 3 shows a possibility of identifying various stop elements bymeans of magnets and Hall elements,

[0047]FIG. 4 shows a further possibility of identifying various stopelements by means of electronic memory chips,

[0048]FIG. 5 shows an overall diagram of a device according to theinvention, comprising distance-measuring instrument and stop element forconnection to a holder,

[0049]FIG. 6 shows the possible movements of the total system comprisingthe device and a stand mount, shown by way of example, as a holder,

[0050]FIG. 7 shows the function and the prevailing geometric conditionsof the device according to the invention, comprising a stop element forconnection to a holder, with a vertical difference between measuringpoints,

[0051]FIG. 8 shows the function and the prevailing geometric conditionsof a comparable device of the prior art, with a vertical differencebetween measuring points,

[0052]FIG. 9 shows the different geometric conditions in the case of adevice according to the invention, comprising a stop element forconnection to a holder, and in the case of a device of the prior art.

[0053]FIG. 1 shows the possibility of mounting a first stop element 3and a second stop element 3′ on a distance-measuring instrument 1. Theexchangeable mounting is effected here, by way of example, on the sidewhich is opposite the emission of a laser beam 2, but mounting atanother location of the distance-measuring instrument 1 is not ruled outherewith. The first stop element 3 and the second stop element 3′ havebeen optimized for different surfaces. Here, a first stop element 3having an installation spike 4 for installation in holes or angles and asecond stop element 3′ having a curved recess 4′ for installation onpipes or other spherically shaped bodies are shown by way of example. Anadjustable design of the curved recess 4′ permits installation onsurfaces having different radii of curvature.

[0054]FIG. 2 shows, by way of example, the use of the second stopelement 3′ for defined installation of the device according to theinvention on a curved installation surface, for example a pipe A.Defined positioning of the distance-measuring instrument 1 relative tothe pipe A can be achieved by a mechanically strong connection betweenthe two parts of the device, i.e. distance-measuring instrument 1 andsecond stop element 3′.

[0055] The identification of the first stop element 3 or second stopelement 3′ by the distance-measuring instrument 1 can be effected, forexample, by the use, shown in FIG. 3, of magnets 5 and Hall elements 7.In the first stop element 3 or second stop element 3′, magnets 5 aremounted at different positions unique to the respective stop element.The magnetic field is made detectable for the Hall elements 7 bymagnetic field conductors 6 in the distance-measuring instrument 1. Inthe examples shown, in each case only one of the two Hall elements 7detects a magnetic field which is generated by the magnets 5 mountedspecifically for the first stop element 3 or second stop element 3′.Thus, the unique identification of the first stop element 3 or secondstop element 3′ is possible solely by the determination of the signal ofone of the two Hall elements.

[0056] Another possibility is the identification, shown in FIG. 4, bymeans of memory modules 8. The first stop element 3 and second stopelement 3′ each contain a memory module 8, for example an electronicone, in which the data specific to the first stop element 3 and secondstop element 3′ are stored. These data can be transmitted as anelectromagnetic signal 11 and received and further processed byelectronics 9 present in this example in the distance-measuringinstrument 1.

[0057]FIG. 5 schematically shows a device according to the inventionwith the use of a stop element as a stop element, consisting of a laserdistance-measuring instrument 1, which is fastened on its side oppositethe laser beam 2 to an exchangeable stop element 3″, and a stand shownby way of example here as a tripod. The connection between laserdistance-measuring instrument 1 and stand mount 13 is effected via thestop element 3″ rotatably mounted at the point of intersection B of ahorizontal axis 12 and a vertical axis. The axes of the laser beam 2 andof the laser detector 2′ are coaxial or are close together and passthrough or in the immediate vicinity of the point of intersection of theaxes of rotation.

[0058]FIG. 6 shows the possible rotations of the components laserdistance-measuring instrument 1 and stop element 3″, which are connectedto one another, about a horizontal axis of rotation 12 and a verticalaxis of rotation 12′.

[0059]FIG. 7 shows the use of the device according to the invention andof a stand mount, shown by way of example, for measuring the heightdifference between a lower measuring point C and an upper measuringpoint D. The device consisting of distance-measuring instrument 1 andstop element 3″ is connected at the point of intersection B of thevertical and horizontal axes of rotation 12 to the stand mount 5 so asto be pivotable about the horizontal axis of rotation 12. After ameasurement of the distance to the measuring point C by means of laserbeam 2, the device is rotated about the horizontal axis of rotation 12and the distance to the upper measuring point D is measured in anidentical manner. From knowledge of the two distances and of the anglein between, the height difference can be calculated.

[0060]FIG. 8 shows a similar procedure using a device of the prior art.The horizontal axis of rotation 12 of the laser distance-measuringinstrument 1 is now substantially below the axis of the laser beam 2.

[0061] The exact conditions and the differences between the two devicesare shown in FIG. 9. In FIG. 9a, vertical and horizontal axes ofrotation 12 coincide with the longitudinal axis 14 of the laserdistance-measuring instrument 1 and of the stop element 3″ at the pointof intersection B. Here, the longitudinal axis 14 is parallel to thelines of sight of the distance measurements and in their immediatevicinity. In the device of the prior art which is shown in FIG. 9b, thelongitudinal axis of the laser distance-measuring instrument 1 isoutside this point of intersection of vertical and horizontal axes ofrotation 12. If the base of the laser distance-measuring instrument 1,which is opposite the exit aperture of the laser beam, is now taken as areference point, a correction 17 has to be taken into account aftertilting of the laser distance-measuring instrument from the firstmeasuring position 15 to the second measuring position 16 for themeasured distance since the reference point has changed with respect tothe distance to the point of intersection B. List of reference numerals 1 Distance-measuring instrument  2 Laser beam  2′ Laser detector  3First stop element  3′ Second stop element  3″ Third stop element  4Installation spike  4′ Curved recess  5 Magnet  6 Magnetic fieldconductor  7 Hall element  8 Magnetic field lines  9 Memory module 10Electronics 11 Electromagnetic signal 12 Horizontal axis of rotation 12′Vertical axis of rotation 13 Stand mount 14 Longitudinal axis of thelaser distance-measuring instrument 15 First measuring position 16Second measuring position 17 Correction A Pipe B Point of intersectionof the horizontal and vertical axes of rotation C Lower measuring pointD Upper measuring point

1. A device for measuring distances, consisting of a in particularhand-held—distance-measuring instrument (1) and anexchangeable—preferably attachable—stop element (3; 3′; 3″), thedistance-measuring instrument (1) being capable of being positionedspecifically relative to a reference point by the stop element (3; 3′;3″), wherein the stop element (3; 3′; 3″) has an identifier uniquelycoordinated with the stop element, correction means are present fortaking into account the specific positioning relative to the referencepoint in the distance measurement, which positioning is effected by thestop element (3; 3′; 3″), it being possible for these means to bepresent either in the distance-measuring instrument (1), in the stopelement (3; 3′; 3″) or in both.
 2. The device as claimed in claim 1,wherein automatic identification of the stop element (3; 3′; 3″) on thebasis of the identifier is effected by the correction means.
 3. Thedevice as claimed in claim 1 or 2, wherein the correction means comprisemeans for calculation and direct computational correction of a measuredvalue and/or for calculation and indication of a correction value to betaken into account in the measurement, it being possible to specify thevalues relative to the reference point or relative to one or more pointsrelated to this reference point, and the correction means comprisingmeans for selecting the points to be calculated.
 4. The device asclaimed in claim 2 or 3, wherein the identifier consists of at least oneof the following means designed specifically for the respective stopelement (3; 3′; 3″): mechanical, preferably in the form of a plugconnector, electronic, preferably in the form of an integrated circuitor memory module (8), optical, electromagnetic, preferably in the formof a magnetic stripe, magnetic, preferably through mounting of aplurality of magnets (5) and measurement of their position, for examplewith the use of Hall elements (7).
 5. A distance-measuring instrument(1) for a device as claimed in any of the preceding claims, wherein thedistance-measuring instrument (1) has a device by means of which thespecific positioning relative to a reference point is taken into accountin the distance measurement, the positioning being effected by a stopelement (3; 3′; 3″) identifiable on the basis of an identifier uniquelycoordinated with the stop element.
 6. The distance-measuring instrument(1) for a device as claimed in claim 5, wherein for taking into accountthe specific positioning, the distance-measuring instrument (1)comprises means for the computational correction of a measured valueand/or means for indication of a correction value to be taken intoaccount in the measurement, it being possible to specify the valuesrelative to the reference point or relative to one or more pointsrelated to this reference point.
 7. A stop element (3; 3′) for a deviceas claimed in any of claims 1-4, wherein the stop element (3; 3′)defines exact distances between its installation surfaces and a holderfor a distance-measuring instrument (1) and the stop element (3; 3′) hasan identifier uniquely coordinated with this stop element.
 8. The stopelement (3; 3′) as claimed in claim 7, wherein automatic identificationof the stop element (3; 3′) on the basis of the identifier can beeffected by a distance-measuring instrument (1).
 9. The stop element (3;3′) as claimed in claim 8, wherein the identifier comprises at least oneof the following means: mechanical, preferably in the form of a plugconnector, electronic, preferably in the form of an integrated circuitor memory module (8), optical, electromagnetic, preferably in the formof a magnetic stripe, magnetic, preferably through mounting of aplurality of magnets (5) and measurement of their position, for examplewith the use of Hall elements (7).
 10. A stop element (3″) for a deviceas claimed in any of claims 1-4 for fastening a distance-measuringinstrument (1) on a holder, the distance-measuring instrument (1) beingmounted so as to be pivotable at least about one horizontal axis ofrotation (12) relative to the holder, wherein the stop element (3″) isdesigned to be exchangeable, the stop element (3″) defines exactdistances between the holder and the distance-measuring instrument (1)and the distance-measuring instrument (1) is connected by a stop element(3″) to the holder so that an axis of a line of sight used as a distancemeasurement, between distance-measuring instrument (1) and object to bemeasured, or an axis running parallel between a plurality of axes oflines of sight used for distance measurement, between distance-measuringinstrument (1) and object to be measured, intersects the axis ofrotation.
 11. The stop element (3″) as claimed in claim 10, comprisingat least one additional vertical axis of rotation of thedistance-measuring instrument (1) relative to the holder, wherein thedistance-measuring instrument (1) is connected by the stop element (3″)to the holder so that the point of intersection of the two axes ofrotation (B) lies on an axis of a line of sight used for the distancemeasurement, between distance-measuring instrument (1) and object to bemeasured, or between a plurality of axes of lines of sight used for thedistance measurement, between distance-measuring instrument (1) andobject to be measured.
 12. The stop element (3″) as claimed in claim 10or 11, wherein the stop element (3″) has at least two different,settable states with regard to at least one of the followingpossibilities for adjustment: rotation about the longitudinal axis (14)of the stop element (3″), change of the length of the stop element (3″).13. The stop element (3″) as claimed in claim 11 or 12, wherein the stopelement (3″) has an identifier which is uniquely coordinated with saidstop element and by means of which automatic identification can beeffected by the distance-measuring instrument (1).
 14. The stop element(3″) as claimed in claim 13, wherein the identifier comprises one of thefollowing means: mechanical, preferably in the form of a plug connector,electronic, preferably in the form of an integrated circuit or memorymodule, optical, electromagnetic, preferably in the form of a magneticstripe, magnetic, preferably through mounting of a plurality of magnetsand measurement of their position, for example with the use of Hallelements.